In the absence of pressure, volume and temperature (“PVT”) data, it is almost impossible to generate the data files that are needed to conduct a reservoir engineering analysis and, in particular, a numerical reservoir simulation for modeling fluid behavior in hydrocarbon reservoirs. The typical PVT analysis involves collecting down-hole and/or surface samples, conducting quality control tests and then performing either one of a constant mass expansion (CME) or constant volume depletion (CVD) test to create extended black oil tables needed for the reservoir engineering analysis. Even the most popular oil correlations listed in table 1 below do not work reliably with gas condensates (also referred to as retrograde condensates) and wet gases because the extended black oil correlations are generally prone to errors and inconsistencies.
TABLE 1Summary of popular correlations for oil properties showing input requirements and calculated propertiesSymbolInput RequirementsforPres-Temper-GasBubble pointCalculated propertypropertyName of CorrelationsureatureOil_APIGas_GravitySolubilitypressureGas solubilityRsStanding✓✓✓✓Gas solubilityRsVasquez-Beggs✓✓✓✓Gas solubilityRsGlaso✓✓✓✓Gas solubilityRsMarhoun✓✓✓✓Gas solubilityRsPetrosky-Farshad✓✓✓✓Bubble Point PressurePbStanding✓✓✓✓Bubble Point PressurePbVasquez-Beggs✓✓✓✓Bubble Point PressurePbGlaso✓✓✓✓Bubble Point PressurePbMarhoun✓✓✓✓Bubble Point PressurePbPetrosky-Farshad✓✓✓✓Oil Formation Volume FactorBoStanding✓✓✓✓Oil Formation Volume FactorBoVasquez-Beggs✓✓✓✓Oil Formation Volume FactorBoGlaso✓✓✓✓Oil Formation Volume FactorBoMarhoun✓✓✓✓Oil Formation Volume FactorBoPetrosky-Farshad✓✓✓✓Oil Formation Volume FactorBoMaterial Balance Equation✓✓✓✓Isothermal Compressibility of OilcoVasquez-Beggs✓✓✓Isothermal Compressibility of OilcoPetrosky-Farshad✓✓✓Isothermal Compressibility of OilcoMcCain✓✓✓Total Fluid Volume FactorBtStanding✓✓✓✓✓Total Fluid Volume FactorBtGlaso✓✓✓✓✓Total Fluid Volume FactorBtMarhoun✓✓✓✓✓Viscosity of Dead Oilμ_doBeal✓✓Viscosity of Dead Oilμ_doBeggs-Robinson✓✓Viscosity of Dead Oilμ_doGlaso✓✓Viscosity of Sat Oilμ_osatBeggs-Robinson✓✓✓Viscosity of Sat Oilμ_osatChew-Connally✓✓✓Viscosity of Under Saturated Oilμ_uoVasquez - Beggs✓✓✓✓
Therefore, the current trend is to use commercial PVT simulation software to first obtain a mathematically recombined composition, fit the data to an equation of state (EOS) model and create PVT data files for the numerical reservoir simulation in full compositional 7mode. Because this technique can be time consuming and expensive, it is common practice to create reduced compositional models by combining some of the components together and selecting the reduced compositional models that provide a good match with the full compositional models.